We now turn to stating the seed set selection phase, which can be viewed as a generalization of the greedy IM algorithm [1]}. As described in Algorithm 2, the function ModifiedGreedy gradually adds one node maximizing the so-called “marginal expected spread” (see [1]}) to the seed set \(S\) , under the constraint that seed nodes can only be selected from the set of explored nodes, \(\mathcal {V}_T\)  in the graph \(G_\text{gen-prun}^{(T)}\)  (see lines 4 and 6). We note that the expected influence spread \(\hat{\sigma }(\cdot )\)  in line 5 can be approximated via many approaches such as Monte-Carlo simulations, lazy update [3]}, or reverse reachable sets [4]}.
